import { useEffect, useState, FormEvent, ChangeEvent, SyntheticEvent } from 'react'

import TextInput from './TextInput'

export interface InputProps {
  id: string,
  name: string,
  value: any,
  onChange: (event: SyntheticEvent) => void,
  onBlur: (event: SyntheticEvent) => void,
  placeholder: string,
  label: string
}

interface FormHandler {
  inputProps: (name: string) => InputProps,
  handleChange: (event: SyntheticEvent) => void,
  handleBlur: (event: SyntheticEvent) => void,
  values: Dict,
  errors: Dict,
  isSubmitting: boolean
}

/**
 * Provides hooks for forms.
 *
 * @remarks
 * You can use it like this
 * ```ts
 * const {inputParams, formParams} = useFormHandler()
 * ```
 *
 * @param initialValues - Initial values of inputs
 * @param validate - validation function for the form
 * @returns hooks to handle the form
 */
function useFormHandler(
  initialValues: Dict,
  validate?: (values: Dict) => {}
): FormHandler {

  console.log('useFormHandler called.', initialValues)
  const [values, setValues] = useState(initialValues)
  const [errors, setErrors] = useState({})
  const [isSubmitting, setIsSubmitting] = useState(false)

  useEffect(() => {
    if (isSubmitting) {
      const noErrors = Object.keys(errors).length === 0
      if (noErrors) {
        console.log('no errors while submitting.')
      } else {
        console.log('errors while submitting,')
      }
      setIsSubmitting(false)
    }
  }, [errors])

  function handleChange(event: SyntheticEvent): void {
    setValues({
      ...values,
      [(event.target as HTMLInputElement).name]:
        (event.target as HTMLInputElement).value
    })
  }

  function handleBlur(event: SyntheticEvent): void {
    if (validate) {
      const validationErrors = validate(values)
      setErrors(validationErrors)
    }
  }

  function inputProps(name: string, label?: string): InputProps {
    if (!values.hasOwnProperty(name)) {
      throw Error(`${name} is not an existing field.`)
    }
    return {
      id: name,
      name,
      value: values[name],
      onChange: handleChange,
      onBlur: handleBlur,
      placeholder: label || name,
      label: label || name
    }
  }

  return {
    inputProps,
    handleChange,
    handleBlur,
    values,
    errors,
    isSubmitting
  }
}

export { useFormHandler, TextInput }